1. Field of the Invention
The present invention relates to optical devices, projectors, and methods of producing optical devices.
2. Description of the Related Art
Some projectors that employ a laser as a light source use such a diffuser plate as disclosed in Japanese Laid-Open Patent Application No. 2007-233371 in order to correct the intensity distribution of a beam flux emitted from the laser. The diffuser plate, however, diffuses light using random irregularities on its surface, and therefore, is generally inefficient in using light. Thus, optical devices that keep the diffusion of light within a predetermined range by a refraction effect, such as a microlens array, are preferred. Japanese Laid-Open Patent Application No. 2012-145804 discloses using a microlens array in a projector.
In the case of using a highly coherent light source such as a laser, the intensity distribution of a beam flux may be insufficiently corrected with regularly arranged microlenses because diffracted light is generated only in a predetermined direction in accordance with the regularity of the arrangement. As a method for reducing such a diffraction effect, it is known to introduce irregularity to a microlens array. In particular, it is known to diffuse light within a predetermined angular range by introducing irregularity within a controlled range. U.S. Pat. No. 7,033,736 discloses microstructures into which irregularity is introduced in a depth direction, where the range of distribution of microstructures in the depth direction is, for example, 10 μm or more.